Footwork has no built-in method of converting detached footnotes back to live footnotes again (so that they can then be converted to endnotes).
However, the idea is a good one, because I think there could be several advantages of getting Footwork to use endnote text as the footnote text, because it allows for a certain amount of built-in control of the numbering, and if you delete a reference the footnote gets deleted. It also makes it easier, perhaps, to insert new footnotes.
A disadvantage would be that you lose the flexibility Footwork gives you if you need anything beyond simple sequential numbering.
There are a few scripts that attempt to convert text back to footnotes, though.
Peter Kahrel’s: https://creativepro.com/files/kahrel/indesign/endnotes_to_footnotes.html
And Jongware’s script which he posts in this forum topic, but read the instructions carefully: https://community.adobe.com/t5/indesign/loosing-footnotes-when-placing-word-in-indesign/td-p/5128955
I’ll be interested to know if you get either of those to work!